MAINTENANCE AND CERTIFICATION
- ISSUE 3/2008
- Copyright and Credits
- Guest Editorial
- To the Letter
- Flight Operations
- Maintenance and Certification
- Recently Released TSB Reports
- Accident Synopses
- Regulations and You
- The Civil Aviation Medical Examiner and You
- Debrief: The Luck Meter—Don't Leave Home Without It!
- Don't Let It Get This Far! Runway Incursions Are Real! (poster)
- Full HTML Version
- PDF Version
- New Manufacturing Regulations
- Icing in Fuel Injection System Distribution Manifolds
- Top-Level Inspections!
- Issues with FDR and CVR Data Identified as a Result of TSB Reviews
- HeadsUp! Airplane Design and Operations in Icing Conditions
On December1, 2007, the new Canadian Aviation Regulations (CAR)561 came into effect. This is a major milestone in the introduction of the CARs and one of the final stages in the replacement of the old Airworthiness Manual with the new CARs. The new requirements are very similar to those of the earlier Airworthiness Manual but, being regulations, they are more formal in structure, and unlike the Airworthiness Manual, are directly enforceable. Many of the sections have been identified as designated provisions, with maximum penalties established for both individuals and corporations.
Along with the introduction of CAR561 itself, there was an associated standard (STD561) and changes in PartI of the CARs to enable the application of safety management systems (SMS) to manufacturers. Changes to the definitions of "maintenance" and "manufacture" should eliminate any conflict between the application of CARs561 and571. Essentially, CAR561 will apply to any work performed on an aircraft prior to the first issuance of a standard certificate of airworthiness or export airworthiness certificate. Following the issuance of either of those certificates, CAR571 will apply. For example, the making of a repair part under CAR571.06(4) will be exempt from any of the provisions of CAR561.
The privilege of a manufacturer certificate is not actually to manufacture aeronautical products-anyone may do that-but rather, to authorize the issuance of a statement of conformity attesting that the products conform to approved data, and are in condition for safe operation. CAR571, in turn, prohibits the installation of parts (other than commercial or standard parts, and parts made during the course of a repair) unless they have been certified with such a statement. The statement in question usually takes the form of the familiar Authorized Release Certificate (form 24-0078, soon to be retitled Form One). The repair parts mentioned above may not be released on a Form One, but instead are certified by means of the maintenance release covering the repair for which they were created.
The new regulations follow the same general format as the approved maintenance organization (AMO) requirements of CAR573. They provide for separate production control and quality audit systems, and include requirements for training and record keeping. Issuance of a manufacturer certificate is directly tied to the applicable aeronautical product type certificate. Applicants must either hold the type certificate personally, or have entered into a licensing agreement with the holder. A limited approval may be granted if the type certificate has not yet been issued, or where the licensing agreement is still being negotiated; however, in such cases, the finished products may not be released until the type certificate provisions have been fully met.
The regulations specify a manufacturer’s responsibility for the control of suppliers, and make a clear distinction between the oversight of suppliers who are approved in their own right, and suppliers who work under the umbrella of the prime manufacturer. This should facilitate the control of "direct delivery", which may only be authorized in conjunction with a release certificate.
Manufacturer facilities may be located in a foreign state, subject to the agreement of the foreign authority, but the applicant must undertake the responsibility to allow Transport Canada inspectors access to the foreign facilities, and pay for the expenses incurred.
The manufacturer’s means of compliance with the various requirements must be set out in a manual that is signed by the accountable executive and approved by the Minister.
Unlike the introduction of some previous CARs, such as those relating to air operators and AMOs, there will be no grace period enabled by exemption. When earlier chapters were incorporated into the CARs, the new requirements were published as soon as they were available, and a general exemption was issued to enable certificate holders to transition to full compliance over a period of time, in accordance with a predetermined implementation program. In this instance, the process has been reversed. Existing approval holders were notified of the new requirements some two years in advance of the effective date, and they must be in full compliance with them on that date.
With the introduction of CAR561, the implementation of airworthiness-related CARs is almost complete. The final major piece of the puzzle will be CAR563, applying to distributors of aeronautical products. That chapter is expected to be incorporated into the CARs later in2008.
On November30, 2007, an Aero Commander500B departed from Dryden,Ont., en route to Geraldton,Ont., with a crew of two and one passenger. Approximately 40 min after departure, the crew observed an abnormal right engine fuel flow indication. Shortly thereafter, the right engine’s RPM and fuel flow began to decrease. The crew diverted towards Armstrong, Ont. A short time later, the left engine RPM and fuel flow began to decrease and the aircraft could no longer maintain level flight. The crew made a forced landing into a marshy wooded area 20NM southwest of Armstrong. The captain sustained serious injuries and the co-pilot and passenger sustained minor injuries. The aircraft sustained substantial damage. The investigation into this occurrence (TSB File A07C0225) is ongoing.
An examination of the LycomingI0-540-B1A5 engines determined that there was a blockage in the fuel supply to both engines. The left engine had a partial blockage with no fuel supply to the forward cylinder nozzles; the right engine had a complete blockage with no fuel supply to any of the cylinder nozzles. The blockage was determined to be within the fuel distributor valve(s) because fuel pressure was present upstream of the valves. The right engine fuel distributor valve was removed and examined. There was ice found adhering to the internal main metering well surface. Ice formed from super-cooled water droplets was also found adhering to the servo bleed screen, fully covering and blocking the return-to-tank bleed orifice.
The aircraft had been stored in a heated hangar and had been fully fuelled from a commercial fuel supplier, approximately two months prior to the occurrence. The fuel tanks and strainers were drained during the pre-flight inspection and no visible water was noted. The aircraft was operated without a fuel additive icing inhibiter.
Fuel distributor valve installation in the lower front engine area
Ice on main metering well
Super-cooled droplet ice-formation on the servo bleed screen
Return-to-tank bleed orifice (shown frozen and thawed for comparison)
High-altitude testing of piston engines on pressurized aircraft was carried out by a major aircraft manufacturer during the early 1970s1. This testing found that numerous partial and isolated total engine power losses were experienced. The tests concluded that as an aircraft climbed to the colder altitudes, dissolved water in the fuel precipitated out of solution, due to agitation of the fuel as it passed through the fuel pump and/or vapour separator.
The precipitated moisture in the form of super-cooled water droplets emerged from the pump and was carried through the fuel injection metering unit to the fuel distributor valve. A significant reduction in flow velocity occurred at the bottom of the distributor valve plunger well. This, combined with a reduced fuel distributor valve surface temperature (due to the cooling air blast against the forward face of the valve), promoted the formation of ice crystals. These ice crystals continued to capture the supercooled water droplets until the ice build-up blocked the forward fuel injection lines, causing a reduction in engine power. In extreme cases, all the nozzle ports could become blocked, causing a complete loss of engine power. Small ice formations were also observed at the bottom and side surfaces of the fuel distributor plunger (main metering) well. When melted, the ice accumulation represented less than two drops of water. This ice blockage phenomenon was considered capable of affecting most fuel injection systems in service at the time, and was eliminated in part by the adoption of fuel additive icing inhibiters.
The TSB is concerned about the possibility of aircraft engine power loss at low ambient temperatures. Some issues, such as the compatibility of the available fuel icing inhibitors with various aircraft types, have not yet been fully resolved. This investigation is still in progress and findings as to causes and contributing factors have yet to be determined by the Board. Nevertheless, the investigation to date has shown that the freezing of dissolved water, precipitated out of solution in fuel injection system distribution manifolds and related areas, can endanger life and property. Therefore, the aviation community should be aware of the effect of ice in aircraft engines’ fuel systems during winter operations.
Transport Canada may wish to remind operators of the possibility of engine power loss due to icing in fuel systems, and of the importance of following the procedures and precautions contained within aircraft and engine operating manuals for the prevention of fuel system icing in cold weather environments.
by John Tasseron, Civil Aviation Safety Inspector, Aircraft Evaluation, Standards, Civil Aviation, Transport Canada
This is the third and last of three articles on the topic of inspection levels.
Having dealt with the first level of inspection (general visual inspection[GVI]) and the second level (detailed inspection[DET]) of an aircraft maintenance schedule in earlier articles, we are now ready to look at the last and highest level, namely the special detailed inspection, or SDI. Since only a small percentage of the total number of inspection tasks in an aircraft maintenance schedule fall into the SDI category, and since these tasks are typically performed long after the aircraft has entered service, SDIs are not well known. Luckily, we have the Air Transport Association of America (ATA) definition to help us out:
"An intensive examination of a specific item, installation or assembly to detect damage, failure or irregularity. The examination is likely to make extensive use of specialized inspection techniques and/ or equipment. Intricate cleaning and substantial access or disassembly procedure[sic] may be required."
If we compare the above definition to that of a detailed inspection, we see that the first sentences are identical. The word "intensive" clearly translates into "looking for small irregularities." The rest of the definition is completely different. No mention is made of lighting requirements. Instead, the emphasis is on "extensive use of specialized inspection techniques and/or equipment," "intricate cleaning" and "substantial access or disassembly." Some of this terminology needs explaining.
Currently, some newer inspection technologies also appear to qualify for SDI status. These often fall outside of the traditional NDI realm and do not require the use of specially-certified personnel. The most prominent one of these involves procedures that include the application of borescope technology. Borescope inspection falls somewhere between visual inspection with the naked eye and inspection done with complex specialized test equipment. In some cases, during the construction of an aircraft maintenance schedule to ATA standards, the working groups doing the maintenance analysis made decisions to allocate the DET level to all borescope inspection tasks, while in other cases, these tasks were deemed to be SDIs. The logic supporting classification to a DET included the fact that borescope inspections usually concentrated on small areas; the logic supporting an SDI classification came from the fact that special procedures and training of specialists were required. The discussion is still on-going.
It matters little what inspection level is assigned to the task, as long as it is clearly spelled out what must be done. If a borescope inspection is classified as an SDI or a DET, and is then performed by a person who has no borescope inspection training or special instructions, the level of inspection performed may be no better than that of a GVI. Incidentally, new initiatives are underway to apply the latest borescope technologies to large-area (GVItype) inspections of inaccessible areas, such as the internal surfaces of flight controls. Perhaps some new ideas, such as a new inspection level with its own term and definition, may appear (remote visual inspection, or RVI?). Again, there will be room for argument, and it will be necessary to ensure that whatever is chosen will be clearly explained. In the meantime, the understanding of the currentlyused terms and definitions will have to be relied upon to maintain consistency.
Issues with FDR and CVR Data Identified as a Result of TSB Reviews
by Dave White, Civil Aviation Safety Inspector, Aircraft Maintenance and Manufacturing, Prairie and Northern Region, Civil Aviation, Transport Canada
Annual requirements to maintain cockpit voice recorder (CVR) and flight data recorder (FDR) systems are not being consistently and effectively applied. Sometimes the previous intelligibility test (CVR) and correlation check (FDR) results are not available from the aircraft records. This lack of information is usually not discovered during an annual review of company records or during an aircraft import process. In all cases, data available to the investigators from the black boxes at the time of an accident or incident may not be as readable or ultimately useful as it could be. To address this data issue, let us look at these two very different-but related-black box system annual inspection requirements.
CVR Issue: Transportation Safety Board of Canada (TSB) investigations following accidents and incidents have revealed discrepancies with available CVR recordings. These issues are often related to the quality of the recording channels-an element that could have been previously identified and rectified through the annual inspection requirements.
CanadianAviationRegulations CARs Standard625 AppendixC15(d) states that:
"d) An intelligibility check shall be performed by means of a test procedure which, when completed under operational conditions, shall enable verification of intelligible recorded audio information from all the various input sources required by the regulations:
- upon initial installation;
- at every 3,000 hours, or 12 months, whichever comes first.
The purpose of the CVR intelligibility test is to ensure "intelligible recorded audio information from all the various input sources." With this in mind, it is the aircraft sources and their interconnection, as well as the black box, that affect the intelligibility. Often, the discrepancies are with the peripherals and the interconnection, as opposed to the unit (black box) itself. Examples include: poorly-positioned area microphones that are covered in the actual day-to-day operations of the aircraft; crossed microphone wires that will not noticeably affect the microphone performance but will cause cancelling on the CVR summing and less-than-acceptable performance of channels that does not get rectified even after identification.
Since this inspection is not based solely on the CVR unit itself, but rather the state of the recordings, it is important to have a test procedure that addresses all areas of the inspection:
- an easy-to-follow descriptive checksheet;
- a means of scheduling the test to ensure that sufficient time is allowed to have the recording verified before the next 12-month intelligibility check is due;
- a means of ensuring timely communications with the readback facility to quickly identify issues with the system;
- a two-part process to ensure that issues identified during the playback of the recording, as well as issues with the CVR unit, are addressed through the company defect rectification system;
- a means to ensure that issues requiring rectification are addressed and an intelligibility test is completed to verify that all parameters are recording as required at the end of the process.
FDR Issue: TSB investigations following accidents and incidents have revealed discrepancies with the FDR data available. These issues are often related to missing or unreadable parameters of the FDR system that should have been previously identified and rectified through the annual correlation check requirements. Sometimes the previous correlation test results were not available or attained during the import process.
CARs Standard625 AppendixC 17-FDR Maintenance Schedule states in part:
Correlation check to ensure all required
parameters are being recorded and usable.
12 months, whichever occurs first
The purpose of the FDR correlation check is to ensure "all required parameters are being recorded and usable." With this in mind, it is the aircraft inputs, their interconnection and the black box itself that affect the usability of the data. Often, the discrepancies are with the peripherals and the interconnections, as opposed to the unit (black box) itself. Additionally, continued correlated positions and data readout for known flight control position or other input position must be ensured on FDR readings. For example, position transmitters can be moved from their previous null value during flight control maintenance. Following the maintenance, the flight control continues to operate normally; however, the associated position readings are no longer accurate for previously recorded data. There are some incidents of parameters not being recorded at all due to various malfunctions. In extreme cases, the annual correlation, which was needed to determine the serviceability of the parameters, was not being conducted at all. The purpose of this correlation is to determine the observed relationship between the annual readings and those taken at the time of installation of the devices.
Since this inspection is not based solely on the FDR unit itself, but rather the state of the inputs, it is important to have a test procedure that addresses the following issues:
- access to the tools required to complete the tasks for the inputs;
- access to the last correlation readout; an original installation correlation report may be appropriate here, but be aware-some changes may have occurred since the installation;
- access to the original installation readouts and tolerances allowed;
- a process to ensure that issues identified during the reading of the download, as well as issues with the FDR unit, are addressed through the company defect rectification system;
- a means to ensure that input issues requiring rectification are addressed and a complete correlation check is completed to ensure that all parameters are recording prior to the required 12-month due date.
Regulations are in place governing the requirement to maintain CVR/FDR systems. This brief overview of the purpose and means of conducting an "intelligibility" test and a "correlation" check will hopefully prompt you, as an operator or maintainer, to revisit your last CVR/FDR results. If these results are not available or contain discrepancies, such as unclear CVR channels or nonfunctioning FDR parameters, do your part to ensure that black box systems meet the CARs requirements by locating these results or redoing the test without delay. Also, remember that when importing an aircraft, you must ensure that the appropriate data was recorded and is available, and that the systems meet the current requirements.
Heads Up! Airplane Design and Operations in Icing Conditions
by Michael Hamer, Senior Engineer, Powerplants and Emissions, Engineering, National Aircraft Certification, Civil Aviation, Transport Canada
Engine icing due to ice crystal and mixed phase conditions
When certifying an airplane for flight in icing conditions, many design, flight performance and handling characteristics need to be addressed, including those that apply to the powerplant. The design standards in Chapter525 of the Airworthiness Manual (AWM) include a definition of the atmospheric icing conditions (in Appendix C1), which are defined by the variables of the cloud liquid water content (LWC), the mean effective diameter (MVD) of the cloud drops, and the ambient air temperature (from 0°C to -40°C). The limits of Appendix C include liquid water drops up to 50 microns MVD in size and typically at altitudes of up to 22 000 ft. In Chapter533 of the AWM, additional design standards are specified for engine certification to conditions such as rain and hail.
Mixed phase conditions occur when super-cooled liquid water drops, or SLD, as referred to in Appendix C, and ice particles co-exist in a cloud, often around the outskirts of a deep convective cloud formation. Ice crystal icing exists when all of the liquid water drops in the cloud have frozen into ice particles, typically occurring at the higher flight altitudes. Mixed phase/ice crystal conditions are also outside the present AppendixC icing environment.
Ice crystal/mixed phase icing threat to engines-In-service events
In support of the IPHWG mandate, the engine subgroup of the government and industry committee, the Engine Harmonization Working Group (EHWG), studied over 60 large transport airplane engine power loss events that occurred between 1988 and 2005 due to engine icing in ice crystal with mixed phase conditions. The engines exhibited various symptoms, including vibrations, flameout, rollback, surge and core blade damage. Over two-thirds of the events occurred at altitudes between 22 000 and 39000 ft. At these high altitudes, water is most likely to exist in the form of frozen ice particles or crystals rather than super-cooled liquid water drops. In general, these engine events occurred near convective clouds at ambient temperature warmer than the International Standard Atmosphere (ISA) and outside the current AppendixC of Chapter525 of the AWM certification envelope. These events affected multiple models of airplanes and engines. The events occurred in climb, cruise and descent.
The ice crystal or mixed phase icing threat to engines is a major concern since engines are relied upon to continue to operate in any kind of icing conditions.
Previously, a commuter type airplane suffered engine rollback events at altitudes between 28000 and 31 000feet. Extensive investigation, including flight testing, led to the understanding that ice particles were accreting on warm surfaces in the engine core. In 2003, the EHWG compared the commuter airplane events to the large transport events. Based on this comparison, the industry has recognized that these high altitude large transport airplane engine events are most likely due to ice particle or crystal icing.
Analysis by the engine manufacturers determined that ice particles can accrete further aft (in the core) of the engine, resulting in effects not seen during certification testing with super-cooled liquid water, rain, or hail. In addition, these engine events seemed to involve no significant observations of any appreciable airframe icing, nor were there any ice detector responses, if installed. However, malfunctioning of the total air temperature (TAT) probe occurred during many of the engine events and is now a known indicator of ice particle or crystal accretion in engines. The events typically occurred in visible moisture conditions in cloud with light to moderate turbulence. Pilots report precipitation on the windscreen, often described as "rain" and no weather radar echoes at the location and altitude of the airplane engine event.
The ice crystal or mixed phase icing threat to engines is a major concern since engines are relied upon to continue to operate in any kind of icing conditions, even if the airplane is not certified for flight in those conditions.
Deep convective clouds
Deep convective clouds can lift high concentrations of water thousands of feet into the atmosphere. This warm, humid air is rapidly lifted to high altitudes where the very low ambient temperatures result in ice particle/crystal formation. In theory, the ice water content can be four times greater than the certification standard for super-cooled liquid water. Limited measurements exist of the microphysical properties of deep convective clouds. Existing measurements are confounded by uncertain accuracy of ice water content measurements. Ice particle or crystal size may be concentrated at much smaller sizes than previously thought.
Hypothesis of ice accretion mechanism
Frozen ice crystals bounce off cold surfaces. This explains why airframe icing is not noticed during airplane operation in high altitude ice crystal environments. The physics of ice particle or crystal accretion in the engine is still not completely understood by the industry, but the mechanism is commonly thought to be:
- ice crystals enter engine primary flowpath, upstream surfaces are dry and cooler (below freezing) so there is no accretion;
- at some point in the turbomachinery, air temperatures increase above freezing and warmer surfaces become wetted due to impacts with crystals and their melting into liquid water;
- a combination of further crystal impacts into wet surface layer and evaporation brings the surface temperature back down to the freezing point;
- ice begins to form with further crystal impacts;
- ice can continue to accrete, or it may shed, affecting the engine’s normal operation.
This phenomenon means that ice accretion can occur well behind the fan in the engine core.
Industry challenges-Making the engine more capable
Zones of high ice particle or crystal concentration are not easily identifiable by pilots in-flight, nor are they predicted on weather forecasts. The most effective solution is to make the engine more capable of flight in these conditions. Flight research measurements of these conditions are needed to characterize the ice particle/ crystal environment. Facilities for testing engines in these conditions do not exist and need to be developed. Manufacturers also need to conduct more research into the physics of the ice particle or crystal accretion and shedding mechanisms within the engine, as this is still not fully understood.
Government and industry committee (EHWG) activities
In support of the work done by the FAA ARAC IPHWG committee, the EHWG committee has created a draft AppendixD to FARPart33, Airworthiness Standards: Aircraft Engines, for the ice crystal envelope, and has written draft rules and guidance for engine compliance in the ice crystal environment. The committee has also written a Technology Plan (Research and Regulatory Road Map) to address the industry challenges. The work of these two committees has been submitted to the FAA through the ARAC process for consideration and possible future regulatory directions.
Looking for AIP Canada (ICAO) Supplements
and Aeronautical Information Circulars (AIC)?
As a reminder to all pilots and operators, AIP Canada (ICAO) supplements
and AICs are found on-line on the NAVCANADA Web site (http://www.navcanada.ca/). Pilots and operators
are strongly encouraged to stay up to date with these documents by visiting the NAVCANADA Web site,
and following the link to "Aeronautical Information Products."
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